Recently, the downsizing and the capacity expansion of magnetic disk drives have been promoted, and higher recording density has been demanded. In order to increase the recording density, a unit recording area is reduced, and in order to improve the sensitivity for detection of a magnetic signal weakened thereby, techniques for decreasing the floating amount of the magnetic head are being developed. In order to decrease the floating amount of a magnetic head and ensure recording areas, a magnetic disk substrate has to fulfill severer requirements, such as the improvement of smoothness and flatness typified by the reduction of surface roughness, waviness, and edge rounding, as well as the reduction of defects typified by the reduction of scratches, projections, pits, etc. To cope with these requirements, a polishing liquid composition containing a copolymer having a functional group such as a carboxyl group or a sulfonic acid group has been proposed (e.g., JP 2010-135052 A, and JP 2010-170650 A).
JP 2010-135052 A discloses an abrasive composition that uses an anionic surfactant having a repeat unit and a sulfonic acid (salt) group in a molecule, and further having an aromatic group in a main chain of the repeat unit, thereby enabling reduction of defects such as scratches, and enabling efficient polishing since foaming less in a polishing process.
JP 2010-170650 A discloses a polishing liquid composition for magnetic disk substrates that contains a water-soluble polymer having an anionic group, and thereby making it possible to provide a polished substrate with reduced scratches and surface roughness, without impairing productivity.